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Site Status

EPA has recently completed the third five-year review (PDF) (40 pp, 15.5 MB) of the site and concluded that the cleanup remedies remain protective of human health and the environment.

EPA has worked with the potentially responsible parties via a consent decree to remediate the site.

On August 19, 2002, EPA conducted the final on-site inspection of a finished museum parking lot. This parking lot was built as part of the site cleanup, and the lot will function as a cap to contain the contaminated soils. The parking lot and its nearby perimeter were graded and seeded.

In early 2005, PRP First Energy (formerly General Public Utilities Corporation) completed a groundwater investigation to define the extent of the perchloroethene contamination. EPA formally accepted the results of this study in December 2005 and used it to plan a site-wide supplementary groundwater investigation, intended to fill any remaining data gaps.

EPA completed groundwater sampling for the first phase of this investigation in April 2006, and completed the second phase of groundwater sampling in January 2008.

Vapor Intrusion sampling is done to determine if there is any risk of contaminated vapors entering a building from the soil beneath and around the building. EPA conducted an initial round of vapor intrusion testing at several locations in Dover in April 2008 and found no significant risk posed by vapor intrusion at the site.

EPA finished a Five-Year Review for the first cleanup at the Site in July 2009 and just recently completed the third and final phase of the groundwater investigation in October 2009.

A second vapor intrusion study was completed in 2010 and likewise showed no significant vapor intrusion issues at the Site. EPA completed the third and final phase of its supplementary investigation of groundwater contamination beneath the City of Dover in 2011. EPA expects to complete the human health and ecological risk assessments at the Site in 2014.

Background

The one-acre Dover Gas Light Co. Site originally began as a coal gasification plant in the City of Dover.

Approximately 10,000 people live within one mile of the site and an estimated 45,000 people are served by public and private wells within three miles of the site.

From 1859 to 1948 the Dover Gas Light Co. produced gas from coal. This gas was used for street lamps and other purposes.

Upon closing of the plant in 1948, all of the structures except a brick garage were demolished. Much of the plant was removed, but sections of the tanks and other process equipment were buried on site. These underground structures contained coal oil and/or coal tar.

In 1984, remains of the coal gasification plant were found.

For several years the site was used as an unpaved parking lot for a museum next door. That parking lot area is now paved.

A cemetery and historic church are located on the same block.

Seven of Dover's 14 municipal supply wells are located within one mile of the site; however, the Dover municipal system draws water from a lower, uncontaminated aquifer.

The municipal wells were sampled in 1988 and 1991 and did not show signs of contamination. These wells were sampled again during the supplementary groundwater investigation currently underway. No site-related contamination was found.

Cleanup History

NPL Listing History

On January 22, 1987 this site this site was proposed to the National Priorities List of the most serious uncontrolled or abandoned hazardous waste sites requiring long-term cleanup action.

On October 4, 1989 the site was formally added to the list, making it eligible for federal cleanup funds.

EPA's decisions on how to address site contamination are formally outlined in legal documents known as Records of Decision. The first Record of Decision (ROD) for this site was issued on August 16, 1994. In it, EPA called for the excavation of contaminated soils and off-site treatment. Also, EPA selected a combination of containment and natural attenuation for the groundwater.

In May 1995, EPA ordered Chesapeake Utilities Corporation and to General Public Utilities Corporation, ordering them to implement the ROD. Only Chesapeake Utilities Corporation complied with this May 1995 order.

In December 1997, EPA modified the soil cleanup requirements. Contaminated soil would be excavated from within the three underground brick structures called gas holders. Remaining soil contamination would be addressed by using soil vapor extraction (SVE) technology and capping the one-acre lot with an asphalt parking lot.

On April 25, 2002, Chesapeake Utilities Corporation (CUC) began the parking lot construction. The parking lot construction, among other things, restricts exposure to soils and limits storm water infiltration in soils. CUC completed soil cleanup work in September 2002. EPA completed its second five-year review on this remedy in July 2009.

In 2000 design for the groundwater containment system was stopped to further reconsider the releases of perchloroethene from a nearby dry cleaner. First Energy (formerly General Public Utilities Corporation) completed a groundwater investigation to define the extent of the perchloroethene contamination. EPA formally accepted the results of this study in December 2005.

EPA used the 2005 ground water investigation completed by First Energy to plan a site-wide supplementary groundwater investigation, intended to fill any remaining data gaps.

EPA completed groundwater sampling for the first phase of this investigation in April 2006, and completed the second phase of groundwater sampling in January 2008.

EPA also conducted an initial round of vapor intrusion testing at several locations in Dover between April and July 2008.

EPA finished the second Five- Year Review for the first cleanup at the Site in July 2009.

A second vapor intrusion study was completed in 2010. EPA completed the field investigation of groundwater contamination beneath the City of Dover in 2011.

Contaminants and Risks

Specific contaminants detected in the groundwater and soil include volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene, and xylenes, and polynuclear aromatic hydrocarbons (PAHs) or creosote-type compounds from former site activities. Releases of perchloroethene (a dry cleaning solvent) and trichloroethene (a known perchloroethene breakdown product) from a nearby dry cleaner have also contributed to the groundwater contamination at this site.